This allows building sourcekitd and swift-refactor with `SWIFT_BUILD_SWIFT_SYNTAX=NO`. In these builds, the `relatedidents` and `find-syntactic-rename-ranges` requests will always return an error.
I will remove the `syntactic-rename` refactoring action in a follow-up commit. Clients should always ask for rename ranges and perform the rename by themselves instead of asking for a renamed file.
A label range of 0 length was being reported as the label of trailing closure
arguments, just before the opening '{'.
For the rename refactoring, this meant that if the corresponding parameter had
an external label (e.g. 'a') the occurrence would be treated as not matching the
expected symbol name, and so not be updated at all.
For the migrator, when renaming a function with an unlabelled closure for its
last parameter to have a label, it would incorrectly insert the new label in
front of the opening '{' on all of that function's callsites with trailing
closures.
Resolves rdar://problem/42162571
This converts the instances of the pattern for which we have a proper
substitution in lit. This will make it easier to replace it
appropriately with Windows equivalents.
